Method for characterizing detection path in charged particle beam system and charged particle mirror

Abstract

A method of characterizing a detection path in a charged particle beam system having a primary charged particle beam includes positioning a charged particle mirror having a curved equipotential plane on a sample stage of the charged particle beam system; changing the reflection angle of the primary charged particle beam at a curved equipotential surface by changing the relative mirror position of the charged particle mirror, the curved equipotential surface being at a distance from the surface of the charged particle mirror; recording a plurality of detector signals of at least one detector of the charged particle beam system for the plurality of relative mirror positions; wherein varying the relative mirror position of the charged particle mirror includes varying at least one of the mirror position of the charged particle mirror and the primary charged particle beam position relative to each other in at least one dimension.

Description

Technical Field

[0001] Embodiments described herein relate to methods for characterizing detection paths in charged particle beam systems, particularly in scanning electron microscopes (SEMs). Specifically, detection paths of signal charged particles at multiple emission angles and emission energies can be characterized. Embodiments further relate to a charged particle mirror configured for use in any of the methods described herein. Background Art

[0002] Modern semiconductor technology places high demands on structuring and probing samples at the nanometer or even sub-nanometer level. Micrometer and nanometer process control, inspection or structuring are usually performed using charged particle beams (e.g., electron beams), which are generated, shaped, deflected and focused in charged particle beam systems (such as electron microscopes or electron beam pattern generators). For inspection purposes, charged particle beams provide superior spatial resolution compared to, for example, photon beams.

[0003] Inspection devices using charged particle beams, such as scanning electron microscopes (SEMs), have many functions in multiple industrial fields, including but not limited to inspection of electronic circuits, exposure systems for photolithography, detection systems, defect inspection tools, and test systems for integrated circuits. In particle beam systems, a fine beam probe with a high current density can be used. For example, in the case of an SEM, a primary electron beam generates signal particles, such as secondary electrons (SE) and / or backscattered electrons (BSE), that can be used to image and / or inspect a sample.

[0004] With a charged particle beam system, a known sample can be used to calibrate the detection path. The known sample can be, for example, a structured silicon wafer or a resolution target. For example, some methods include maximizing and / or increasing the detection signal by optimizing certain optical elements (such as deflectors or lenses) in the detection path.

[0005] The sample emits a large spectrum of signal electrons (secondary electrons and backscattered electrons) at a wide range of emission angles (starting angles of signal electrons from the wafer relative to the wafer normal). The signal collected during maximization and / or augmentation of the detection signal for detection path calibration has a mixture of electrons originating from the sample (e.g., with different angles). Calibrating the detection path with a mixture of signal electrons (i.e., electrons that are not well characterized) provides a poor beam path calibration.

[0006] In view of the above, it would be beneficial to accurately and reliably characterize the detection path of a charged particle beam system. Summary of the invention

[0007] In view of the above, a method of characterizing a detection path in a charged particle beam system and a charged particle mirror configured for characterizing a charged particle beam system are provided according to the independent claims.

[0008] According to one aspect, a method for characterizing a detection path in a charged particle beam system having a primary charged particle beam is provided. The method comprises: positioning a charged particle mirror having a curved equipotential surface on a sample stage of the charged particle beam system; varying a reflection angle of the primary charged particle beam at the curved equipotential surface by varying a relative mirror position of the charged particle mirror, the curved equipotential surface being at a distance from a surface of the charged particle mirror; recording a plurality of detector signals of at least one detector of the charged particle beam system for a plurality of relative mirror positions; wherein varying the relative mirror position of the charged particle mirror comprises varying at least one of the mirror position of the charged particle mirror and the position of the primary charged particle beam relative to each other in at least one dimension.

[0009] According to an aspect, there is provided a charged particle mirror configured for characterizing a charged particle beam system according to any of the methods described herein.

[0010] According to one aspect, a charged particle mirror is provided, comprising: a substrate; a mirror element having a pillar recessed relative to a surface of the substrate; wherein the pillar comprises at least one of the following items: a conductive connection configured to connect the pillar to a voltage source; a conductive element configured to generate a curved equipotential surface when a voltage is applied; and wherein the pillar is rotationally symmetric.

[0011] Embodiments also relate to systems and devices for performing the disclosed methods and include components for performing the various method actions. The described methods may be performed by means of hardware components, computers programmed by appropriate software, by any combination of the two, or in any other manner. In addition, embodiments also relate to methods of operating the described systems and devices.

[0012] Further advantages, features, aspects and details which can be combined with the embodiments described herein are apparent from the dependent claims, the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order that the above-mentioned features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be made by reference to embodiments. The accompanying drawings relate to one or more embodiments and are described below.

[0014] Figure 1 shows a schematic diagram of a charged particle beam system according to embodiments described herein, the charged particle beam system being adapted for operation according to any of the methods described herein;

[0015] Figure 2 Shown in more detail Figure 1 Schematic diagram of a charged particle beam path and depicts a charged particle mirror according to an embodiment of the present disclosure.

[0016] Figure 3 The details of the charged particle mirror at different mirror positions are shown. Figure 2 akin Figure 1 A charged particle beam path of a charged particle beam system.

[0017] Figure 4 An alternative design of a charged particle mirror is shown.

[0018] Figure 5 An alternative design of a charged particle mirror is shown.

[0019] Figure 6 A flow chart depicting a method of characterizing a detection path in a charged particle beam system according to embodiments described herein is shown.

[0020] Figure 7 FIG. 1 shows a diagram illustrating an embodiment according to the present invention with additional optional operations. Figure 6 Flow chart of a method of characterizing a detection path in a charged particle beam system. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to various embodiments, one or more examples of which are shown in the accompanying drawings. In the following description of the drawings, the same reference numerals denote the same parts. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation, but this is not meant to be limiting. In addition, features depicted or described as part of one embodiment may be used on or in conjunction with other embodiments to obtain yet further embodiments. The specification is intended to include such modifications and variations.

[0022] Figure 11 is a schematic diagram of a charged particle beam system 100 for inspecting and / or imaging a sample according to an embodiment described herein. The charged particle beam system 100 includes a charged particle source 105, in particular an electron source, for emitting a primary charged particle beam 11, in particular an electron beam. The primary charged particle beam 11 propagates along an optical axis A of the charged particle beam system 100. The charged particle beam system 100 further includes a sample stage 108 and a focusing lens 120. The focusing lens 120 (in particular an objective lens) focuses the primary charged particle beam 11 on a sample at a sample position on the sample stage 108. In some embodiments, the focusing lens 120 is an objective lens configured to focus the primary charged particle beam 11 on the charged particle mirror 10. In particular, the objective lens can be a magnetic objective lens, an electrostatic electromagnetic lens, or a magnetic electrostatic composite lens. Optionally, the objective lens may include a deceleration field device configured to decelerate the charged particle beam to a predetermined landing energy on the sample, such as one or more deceleration electrodes.

[0023] The charged particle beam system 100 further comprises charged particle detectors 118, 119, in particular electron detectors. The charged particle detectors 118, 119 may be configured to detect signal particles, in particular secondary electrons and / or backscattered electrons, of the signal charged particle beam 12. The charged particle detectors 118, 119 may comprise a plurality of detectors 118, 119 or detector elements.

[0024] The beam optical components of the charged particle beam system 100 may typically be placed in a vacuum chamber 101, which may be evacuated. The primary charged particle beam 11 may typically propagate from a charged particle source 105 toward a sample stage 108 along an optical axis A and at a sub-atmospheric pressure (e.g., less than 10 -3 mbar pressure or less than 10 -5 The sample is struck by a pressure of millibars.

[0025] In some embodiments, a condenser lens system 106 may be arranged downstream of the charged particle source 105, in particular for collimating the primary charged particle beam 11 propagating towards the focusing lens 120. In some embodiments, the charged particle beam system may include a beam influencing element 109 for influencing the primary charged particle beam 11.

[0026] In some embodiments, the charged particle beam system 100 may be an electron microscope, in particular a scanning electron microscope. The scanning deflector 107 may be arranged for scanning the primary charged particle beam 11 over a sample at a sample position of a sample stage 108 .

[0027] The charged particle mirror 10 is placed on a sample stage. The charged particle mirror 10 comprises a substrate 140 and a mirror element 130. The mirror element 130 is supported by the substrate 140 or integrated in the substrate. The substrate 140 may have a plurality of mirror elements 130, in particular a plurality of mirror elements 130 with different designs and / or at different positions. In some embodiments, the surface of the substrate 140 may define a sample plane or an imaging plane. In some embodiments, the mirror element 130 may comprise a curved surface, in particular a spherical surface.

[0028] The sample stage 108 can be moved in at least one dimension, in particular in one dimension of the sample plane. The sample plane is substantially perpendicular to the optical axis A and is the plane in which the sample is positioned in the charged particle beam system 100 to be inspected. The sample stage 108 can be moved illustratively in the x-direction and / or in the y-direction. The sample stage 108 can be moved continuously or stepwise.

[0029] In some embodiments, the charged particle mirror 10, in particular the mirror element 130, may be at an electric potential. In some embodiments, the mirror element 130 may be connected to a voltage source, which may exemplarily allow the mirror element 130 to be set at a predefined electric potential. In some embodiments, the charged particle mirror 10 may be charged using a charged particle beam, in particular a primary charged particle beam 11. The charged particle mirror 10 comprises equipotential surfaces at which the charged particles of the primary charged particle beam are reflected. The equipotential surfaces of the charged particle mirror 10 are at a distance from the surface of the charged particle mirror 10. The equipotential surfaces of the charged particle mirror 10 may be convex or concave. The shape of the equipotential surfaces depends on the charge distribution within the charged particle mirror 10, in particular within the mirror element 130.

[0030] In the embodiments described herein, the detectors 118, 119 detect charged particles, in particular electrons, of the primary charged particle beam 11 after reflection at the charged particle mirror 10. The primary charged particle beam 11 includes charged particles. In the embodiments described herein, the charged particles reflected at the charged particle mirror 10 are regarded as signal charged particle beams 12. The charged particle beam system 100 includes a beam splitter 117 that can separate the signal charged particle beam 12 from the primary charged particle beam 11. Advantageously, the charged particles reflected at the charged particle mirror 10 are used as the signal charged particle beam 12 to characterize the detection path, allowing the use of charged particles reflected at a defined angle. In addition, advantageously, the charged particles reflected at the charged particle mirror 10 are used as the signal charged particle beam 12 to characterize the detection path, allowing the use of charged particles with defined energy. The detection path can be determined by the electromagnetic field between the beam-affecting element (e.g., all beam-affecting elements) and / or the sample or the charged particle mirror 10 and the detectors 118, 119 and / or the beam splitter 117. The detection path may be influenced by optional secondary beam optics.

[0031] The detector signal receiving unit 160 may be configured to receive one or more detector signals of the detectors 118, 119 of the charged particle beam system 100. The detector signal receiving unit 160 may forward one or more detector signals of the detectors 118, 119 to a processing unit 170, which is configured to process the detector signals according to the method described herein. The processing unit 170 may communicate with the sample stage 108. In particular, the processing unit 170 may receive information about the position of the sample stage 108 and may determine the mirror position of the charged particle mirror 10. The processing unit 170 may associate the detector signals received by the detector signal receiving unit 160 from the detectors 118, 119 with the position of the sample stage 108 and the position of the charged particle mirror 10.

[0032] In some embodiments, a method for characterizing a detection path in a charged particle beam system 100 having a primary charged particle beam 11 may include: positioning a charged particle mirror 10 on a sample stage 108 of the charged particle beam system 100, in particular, on an optical axis of the charged particle beam device; the relative mirror position of the charged particle mirror 10 may be changed by scanning the charged particle mirror with the primary charged particle beam in at least one dimension; and recording 630 multiple detector signals of at least one detector 118, 119 of the charged particle beam system 100 for multiple mirror positions; wherein the charged particle mirror 10 includes a curved equipotential surface.

[0033] In some embodiments, a method for characterizing a detection path in a charged particle beam system 100 having a primary charged particle beam 11 may include: positioning a charged particle mirror 10 on a sample stage 108 of the charged particle beam system 100; changing the relative mirror position of the charged particle mirror 10 by changing at least one of the mirror position of the charged particle mirror 10 and the primary charged particle beam position relative to each other in at least one dimension of the sample plane; recording 630 multiple detector signals of at least one detector 118, 119 of the charged particle beam system 100 for multiple mirror positions; wherein the charged particle mirror 10 includes a curved equipotential surface.

[0034] Characterizing the detection path has the advantage of allowing gray level matching. In addition to inspecting and / or imaging the sample with the charged particle beam system 100 based on resolution, matching of the beam path, particularly the signal charged particle beam path, between the sample and the detectors 118, 119 of the charged particle beam system 100 can also be provided. Matching (also referred to as gray level matching) can be beneficial for critical dimension measurement as well as inspection and defect review applications. Gray level matching can also include matching of the sensitivity of the detectors 118, 119.

[0035] After the primary charged particle beam 11 irradiates the sample, secondary electrons (SE) and / or backscattered electrons (BSE) are generated as a signal charged particle beam 12, which carries information about the morphology of the sample, the chemical composition of the sample, the electrostatic potential of the sample and other information. SE is collected and guided to detectors 118, 119, including sensors, especially scintillators, pin diodes, etc. An image is created, in which the grayscale is proportional to the number of charged particles, especially electrons, collected. However, for different sample properties, the detection efficiency, especially the ratio of emitted electrons to detected electrons may be different. In particular, in the charged particle beam system 100, the detection efficiency may be different for different emission angles of the signal charged particle beam 12. Exemplarily, compared with the information charged particles emitted at the second angle, the signal charged particles (such as SE and BSE) emitted at the first angle relative to the primary charged particle beam 11 may have a higher detection efficiency. In addition, compared with the BSE with higher energy, the SE with lower energy may have a higher detection efficiency. The detection efficiency for a particular angle may be different at different charged particle energies and may differ between different charged particle beam systems 100. At a particular angle, the detection efficiency for secondary electrons may be different from the detection efficiency for BSEs.

[0036] The characteristic detection paths as provided by the methods described herein can be further used to better align detection paths in charged particle beam systems 100, particularly in electron microscopes. This can include comparison of detection paths of multiple charged particle beam systems 100. Comparison of detection paths can be used to align multiple charged particle beam systems 100 so that multiple charged particle beam systems have detection paths that are more similar to each other and / or to predefined detection paths.

[0037] A controller 180 may be provided for controlling the charged particle beam system 100. The controller 180 may communicate with the sample stage 108. In particular, the controller 180 may set the relative mirror position of the charged particle mirror 10 by controlling the sample stage 108. The controller 180 may instruct the sample stage 108 to change the mirror position of the charged particle mirror 10 according to a predetermined pattern. The controller 180 may instruct the sample stage 108 to change the mirror position in response to received information (in particular information received from the processing unit 170), in particular in response to signals of the detectors 118, 119 at a specific position of the sample stage 108 and / or a specific position of the charged particle mirror 10. The controller 180 may control the sample stage 108 to change the mirror position in two dimensions, in particular according to a Cartesian coordinate system (with exemplary dimensions x and y) or according to a polar coordinate system (with exemplary dimensions r and φ). The predetermined pattern may ensure a plurality of positions of the charged particle mirror, in particular the entire charged particle mirror 10 measured by the primary charged particle beam 11. This advantageously enables measurement of a variety of reflection angles provided by the charged particle mirror 10. The reflection angle may depend on the energy of the charged particles, in particular the voltage setting of the charged particle source 105 and the energy of the voltage setting of the charged particle mirror 10. The reflection angle may depend on the mirror position of the charged particle mirror 10. Typically, the charged particle energy and the mirror position are well controlled in charged particle beam systems. In typical embodiments, reflection angles between -75° to 75°, -60° to 60° or -45° to 45° may be achieved.

[0038] The processing unit 170 may associate information received from the sample stage 108 about the relative mirror position of the charged particle mirror 10 with respect to the primary charged particle beam 11, in particular the mirror position, with the reflection angle of the primary charged particle beam 11. In particular, the processing unit may associate the position of the charged particle mirror 10 with the reflection angle of a known shape along an equipotential surface of the charged particle mirror 10.

[0039] The controller 180 may further vary the energy of the charged particles of the primary charged particle beam 11, i.e. the landing energy of the primary charged particle beam on the sample (without the mirror). The controller 180 may vary the energy of the charged particles of the primary charged particle beam 11 in a predefined step, in particular in the range of 10 eV to 10 keV. The detector signals of the detectors 118, 119 may be received by the receiving unit 160 at multiple energies of the charged particles of the primary charged particle beam 11. In particular, the detector signals may be received at multiple mirror positions (i.e. the associated starting angles) of the charged particle mirror 10, wherein the charged particles of the primary charged particle beam 11 have multiple energies.

[0040] The controller 180 may map the detector signals of the detectors 118, 119 onto the mirror positions of the charged particle mirror 10. The controller 180 communicates with the charged particle source 105, in particular for controlling the charged particle source 105 and / or receiving information from the charged particle source 105. The controller 180 may receive information about the primary charged particle beam 11, in particular from the charged particle source 105, and may compare the signals detected by the detectors 118, 119 of the signal charged particle beam 12 with the information about the primary charged particle beam 11 to determine the detection efficiency for a specific reflection angle and, for example, the detection efficiency at a predetermined charged particle energy. The controller 180 may control the charged particle beam system 100, in particular the charged particle source 105 and / or the sample stage 108, to record the detection efficiency for a plurality of mirror positions of the charged particle mirror 10 and / or for a plurality of charged particle energies. Exemplarily, the controller may record the detection efficiency in the form of a two-dimensional graph, wherein the detection efficiency of the charged particles is the third dimension.

[0041] The charged particle beam system 100 may be used to inspect and / or image one or more charged particle mirrors 10. In particular, a plurality of charged particle mirrors 10 may be positioned on a sample stage 108 in an imaging plane of the charged particle beam system 100. In some embodiments, the charged particle mirror 10 may include a plurality of mirror elements 130 on a substrate. According to some embodiments, which may be combined with other embodiments described herein, a plurality of primary charged particle beams or a plurality of primary charged particle beams may be characterized using a plurality of charged particle mirror elements disposed on a substrate of the charged particle mirror.

[0042] Figure 2 and Figure 3 The charged particle beam paths are described in more detail. Figure 2 , the reflection of the primary charged particle beam 11 at the charged particle mirror 10 is shown in more detail. The primary charged particle beam 11 propagates along the optical axis A towards the sample stage 108. The charged particle mirror 10 is positioned on the sample stage 108. The reflection point 31 of the charged particle mirror 10, in particular the mirror element 130, at which the primary charged particle beam 11 is reflected, varies depending on the position of the sample stage 108. After reflection, the reflected charged particles form a signal charged particle beam 12, for example above the surface of the mirror element 130, in particular at a certain distance from the physical surface of the surface of the mirror element 130. Depending on the reflection point 31, the primary charged particle beam 11 is reflected at a reflection angle 21. As shown in FIG. Figure 3As shown, by varying the relative mirror position of the charged particle mirror 10 with respect to the primary charged particle beam 11, for example, by moving the sample stage 108, the primary charged particle beam 11 is reflected at another reflection angle 22. By further varying the relative mirror position of the charged particle mirror with respect to the primary charged particle beam, in particular by sampling the surface of the charged particle mirror 10 and the mirror element 130 of the charged particle mirror 10 positioned on the sample stage 108, a plurality of reflection angles of the primary charged particle beam 11 can be measured. Depending on the shape of the mirror element 130, in particular the shape of the curved equipotential surface of the mirror element 130, this may result in the primary charged particle beam 11 being reflected at a plurality of reflection angles. The signal charged particle beam 12 as reflected from the charged particle mirror 10 is detected at a plurality of charged particle detectors 118, and the detection efficiency can be determined for a plurality of reflection angles 21, which are similar to the emission angle when the charged particle beam system 100 is used to measure the sample. When studying a sample using the charged particle beam system 100 , determining the detection efficiency for a variety of reflection angles 21 allows accurate calibration of the signal intensity for multiple emission angles.

[0043] like Figure 2 and Figure 3 As shown, the change in the position of the sample stage 108 with the charged particle mirror 10 causes a change in the reflection points 31, 32 of the primary charged particle beam 11. This causes the reflection angles 21, 22 at which the primary charged particle beam 11 is reflected and subsequently forms the signal charged particle beam 12 to also change. This causes a change in the beam path of the signal charged particle beam 12. For example, in Figure 2 In the embodiment, the primary charged particle beam 11 is reflected and then forms a signal charged particle beam 12 having a component in the positive x direction. After passing through the focusing lens 120, the signal charged particle beam 12 is deflected onto one of the charged particle detectors 118. Figure 3 In the process, the primary charged particle beam 11 is in contact with Figure 2 The light is reflected at different reflection points 32 and at different reflection angles 22 , exemplarily with a component in the negative x-direction. Figure 3 The beam path of the signal charged particle beam 12 in Figure 2 The signal charged particle beam 12 in the charged particle detector 118 is different. Therefore, the charged particle detector 118 (eg, a segmented detector) is detected at different locations. Figure 3 According to some embodiments, different signal beam paths may result in detection of signal charged particles at different locations on the charged particle detector, detection of signal charged particles at different charged particle detectors, or no detection of signal charged particles on the detector.

[0044] In some embodiments, which may be combined with other embodiments described herein, the primary charged particle beam 11 may scan the charged particle mirror 10. In particular, the sample stage 108 may remain in a fixed position and the reflection points 31, 32 of the charged particle beam may vary due to changes in the beam path of the primary charged particle beam 11.

[0045] In some embodiments, the path of the primary charged particle beam 11 may be changed to change the relative mirror position of the charged particle mirror 10 with respect to the primary charged particle beam 11. In particular, the reflection points 31, 32 of the primary charged particle beam 11 may be changed by causing the primary charged particle beam 11 to scan at least a portion of the charged particle mirror 10 (in some embodiments, the entire charged particle mirror 10). The scanning of the primary charged particle beam 11 may be controlled by the controller 180, in particular by controlling the charged particle beam system 100. Exemplarily, the focusing lens 120 may be controlled to change the relative mirror position of the charged particle mirror 10 with respect to the primary charged particle beam 11. In some embodiments, the relative mirror position of the charged particle mirror 10 may be changed with respect to the primary charged particle beam 11 by a combination of a change in the position of the sample stage 108 and a change in the beam path of the primary charged particle beam 11. Exemplarily, a larger structure may be sampled by a change in the position of the sample stage 108, and a smaller structure may be sampled by a change in the beam path of the primary charged particle beam 11.

[0046] In some embodiments not shown in the drawings, in particular at small reflection angles, the primary charged particle beam 11 may be reflected at small reflection angles 21, 22. The signal charged particle beam 12 may have a beam path closer to the optical axis A or substantially parallel to the optical axis A and / or the path of the primary charged particle beam 11. Figure 1 The beam splitter 117 separates the charged particle beam, in particular, the signal charged particle beam 12 from the primary charged particle beam 11. The signal charged particle beam 12 is deflected by the beam splitter 117 and detected by the charged particle detector 119.

[0047] exist Figures 1 to 3 In the embodiment of the present invention, the charged particle mirror 10, in particular the mirror element 130 of the charged particle mirror, has a concave surface. In particular, the mirror element 130 of the charged particle mirror 10 has a concave equipotential surface, and all reflection points 31, 32 are located on the concave equipotential surface. The concave mirror element 130 can be produced on a particularly small scale. In some embodiments that can be combined with other embodiments described herein, the mirror element 130 is rotationally symmetric, in particular n-fold rotationally symmetric, where n is a natural number. In some embodiments, the equipotential surfaces of the charged particle mirror 10, in particular the mirror element 130 of the charged particle mirror 10, are rotationally symmetric, in particular n-fold rotationally symmetric, where n is a natural number. In particular, the equipotential surfaces of the mirror element 130 can be elliptical.

[0048] exist Figure 4 and Figure 5 In FIG. 1 , an alternative charged particle mirror design is shown that can be combined with other embodiments described herein. In particular, in order to solve the large reflection angles 21, 22, 421, 521, a convex charged particle mirror can be used. Figure 4 , a convex charged particle mirror 10 is shown, comprising a substrate 140 and a convex mirror element 430. The equipotential surfaces of the charged particle mirror 10 are recessed relative to the surface of the substrate 140 parallel to the surface of the sample stage 108, in particular, relative to the surface parallel to the sample plane. Figure 4 , the primary charged particle beam 11 is reflected at a reflection angle 421 at a reflection point 431 of the equipotential surface of the charged particle mirror 10. The reflection point 431 may be positioned at a certain distance from the surface of the charged particle mirror 10. The distance between the surface of the charged particle mirror 10 and the equipotential surface, in particular the reflection point 431, depends on the energy of the primary charged particle beam 11 and the potential of the mirror element 130. The convex charged particle mirror 10 may be used in particular to determine the detection efficiency at a large reflection angle 421 representing a large emission angle.

[0049] exist Figure 4 In some embodiments, the mirror element 430 of the charged particle mirror 10 has a convex surface. In particular, the charged particle mirror 10 has a convex equipotential surface, and all reflection points 431 are located on the convex equipotential surface. In some embodiments, the mirror element 430 is rotationally symmetric, in particular, is n-fold rotationally symmetric, where n is a natural number. In some embodiments that can be combined with other embodiments described herein, the equipotential surfaces of the mirror element 430 are rotationally symmetric, in particular, are n-fold rotationally symmetric, where n is a natural number. In particular, the equipotential surfaces of the mirror element 430 can be elliptical.

[0050] exist Figure 5 In the embodiment, the charged particle mirror 10 includes a groove 515 in the substrate 140, and a pillar 531 is positioned in the groove as a mirror element 530. The pillar 531 is recessed relative to the sample plane of the charged particle beam system 100. The pillar 531 may have a main axis that is substantially parallel to the optical axis A of the charged particle beam system 100 and / or to the primary charged particle beam 11. The pillar 531 may be recessed relative to the sample plane of the charged particle beam system 100 so that when the pillar 531 is under potential, the equipotential surface 513 at the center of the pillar 531 is at a height ( Figure 5 In particular, the support 531 may be recessed into the sample plane so that when the support 531 is under potential, the reflection point of the primary charged particle is at a height ( Figure 5 The z direction in the image is basically equal to the sample plane.

[0051] The pillar 531 may be a cylinder, a cone or a truncated cone. The pillar 531 may be rotationally symmetric or may be n-fold rotationally symmetric. The recess 515 may be rotationally symmetric or may be n-fold rotationally symmetric and may have the form of a cylinder, a cone or a truncated cone. Advantageously, the pillar 531 may be produced using MEMS, micro-electromechanical systems, manufacturing methods or conventional semiconductor construction methods, which may imply some deviation from the shapes mentioned above.

[0052] The pillars 531, in particular the geometry of the pillars 531, can be configured to provide a convex or concave equipotential surface 513. A mirror voltage can be applied at the pillars so that the pillars produce a curved equipotential surface of the reflected beam. Since the curved equipotential surface 513 is well defined, it is particularly advantageous to use a charged particle mirror 10 including the pillars 531 as a mirror element 530.

[0053] In some embodiments, the charged particle mirror 10 may be a conductor or may include a conductor. In some embodiments, the mirror element 130, 430, 530 may be a conductor. The potential of the charged particle mirror 10 may be adjusted by a voltage source, which is conductively connected to the charged particle mirror 10 via a conductive connection. The substrate that may support the charged particle mirror 10 may be an isolator that is in particular isolated from the charged particle mirror 10. According to some embodiments, an insulator may be provided between the substrate and the conductive surface of the mirror element 130.

[0054] In some embodiments that may be combined with other embodiments described herein, the charged particle mirror 10 may be insulating. In some embodiments, the mirror element 130, 430, 530 may be insulating. In some embodiments, the mirror element 130, 430, 530 may be conductive, and the substrate 140 of the charged particle mirror 10 may be insulating. Before the measurement of the detection efficiency, the mirror element 130, 430, 530 may be charged by applying a charged particle beam. In some embodiments, the charged particle mirror 10 may be an insulator. In some embodiments, the mirror element 130, 430, 530 may be an insulator. Compared to the primary charged particle beam 11, the charged particle beam used to charge the mirror element 130, 430, 530 until a predefined potential is reached has a higher energy. This advantageously avoids an independent voltage source or feedthrough.

[0055] exist Figure 6 In FIG. 6 , a method 600 for characterizing a detection path in a charged particle beam system is schematically illustrated as a flow chart. Figure 7 A method 700 is shown, comprising: Figure 7In a first operation 610, the charged particle mirror 10 is positioned on the sample stage 108, in particular, the charged particle mirror 10 may be positioned such that an equipotential surface 513 at the center of the charged particle mirror 10, in particular at the center of the equipotential surface of the mirror element 130, is at a height ( Figures 1 to 5 The z direction in the image is basically equal to the sample plane.

[0056] exist Figure 7 In the embodiment of the present invention, after operation 610, if the mirror element 130, 430, 530 is insulating and / or an insulator, the mirror element 130, 430, 530 may be charged with a charged particle beam having an energy exceeding the energy of the primary charged particle beam 11 when used to measure a sample or a charged particle mirror 10. The mirror element 130, 430, 530 is charged until a predefined potential is reached. After reaching the predefined potential, the energy of the primary charged particle beam 11 is set to a level for calibrating the detection efficiency.

[0057] Back to Figure 6 After positioning the charged particle mirror 10 and charging the mirror elements 130, 430, 530 of the charged particle mirror 10, the charged particle beam mirror is probed at a first position of the charged particle mirror 10 using the primary charged particle beam 11, exemplarily by a higher energy charged particle beam as described in operation 715 or by applying a voltage by a voltage source. In order to evaluate multiple positions of the charged particle mirror 10, in particular to obtain multiple reflection angles 21, 22, 421, 521, in operation 620, the position of the sample stage 108 is varied. Varying the position of the sample stage 108 may include varying the position of the sample stage 108 in a predefined pattern. The predefined pattern may ensure that multiple reflection angles 21, 22, 421, 521 of the reflection of the primary charged particle beam 11 are measured. Changing the position of the sample stage 108 may include changing the position of the sample stage 108 in at least two dimensions, in particular, changing the position of the sample stage 108 in at least two dimensions according to a Cartesian coordinate system (with exemplary dimensions x and y) or according to a polar coordinate system (with exemplary dimensions r and φ). In some embodiments, changing the position of the sample stage may include changing the position in a direction parallel to the optical axis A ( Figures 1 to 5 changes in the z direction).

[0058] In some embodiments, in order to evaluate multiple positions of the charged particle mirror 10, in particular to obtain multiple reflection angles 21, 22, 421, 521, in operation 620, the primary charged particle beam position is varied, in particular by scanning the primary charged particle beam 11 across the charged particle mirror 10. Varying the primary charged particle beam position may include varying the primary charged particle beam position in a predefined pattern. The predefined pattern may ensure that multiple reflection angles 21, 22, 421, 521 of the reflection of the primary charged particle beam 11 are measured. Varying the primary charged particle beam position may include varying the primary charged particle beam position in at least two dimensions, in particular varying the primary charged particle beam position in at least two dimensions according to a Cartesian coordinate system (with exemplary dimensions x and y) or according to a polar coordinate system (with exemplary dimensions r and φ).

[0059] For each of a plurality of relative mirror positions of the charged particle mirror 10, a detector signal of the signal charged particle beam 12 (e.g., of each detector) at the charged particle beam detectors 118, 119 is recorded 630. In particular, the signal intensities of the plurality of detector signals and / or the spatial distribution of the signal intensities of the plurality of detector signals are recorded. In order to relate the relative mirror position of the charged particle mirror 10 to the reflection angles 21, 22, 421, 521, the known equipotential surfaces 513 of the charged particle mirror 10 are associated 725 with the relative mirror position of the charged particle mirror 10. For the detector signal at one position of the charged particle mirror 10, the reflection angles 21, 22, 421, 521 are associated with the detector signal.

[0060] In operation 740, a plurality of detector signals at one position of the charged particle mirror 10 are associated with reflection angles 21, 22, 421, 521. Varying the relative mirror position of the charged particle mirror 10 allows mapping of detector signals of the charged particle detectors 118, 119 for a plurality of reflection angles 21, 22, 421, 521 of the primary charged particle beam 11.

[0061] In some embodiments, in addition to the relative mirror position of the charged particle mirror 10, the energy of the primary charged particle beam 11 is varied 726. The energy can be varied by varying the potential of the charged particle source 105. The energy of the primary charged particle beam 11 can be varied for one or more of a plurality of relative mirror positions, in particular for each of a plurality of positions of the charged particle mirror 10 and associated for each of the reflection angles 21, 22, 421, 521 or for some of the positions of the charged particle mirror 10. The different energies of the primary charged particle beam 11 result in a signal charged particle beam 12 with varying energies. This allows characterization of the detection path for different emission energies from the sample. According to some embodiments that can be combined with other embodiments described herein, the mirror element of the charged particle mirror can reflect a focused primary charged particle beam or a charged particle beam that is not focused or not fully focused, for example, in view of the varying energy of the primary charged particle beam. Therefore, embodiments of the present disclosure can be advantageously used to characterize the signal beam path for different primary beam energies.

[0062] In some embodiments, which may be combined with other embodiments described herein, the energy of the primary charged particle beam 11 is changed after the relative mirror position of the charged particle mirror 10 has been changed until a plurality of predefined positions, exemplarily all predefined positions, have been measured, in particular after the relative mirror position of the charged particle mirror 10 has been changed according to a predefined pattern. In some embodiments, which may be combined with other embodiments described herein, the energy of the primary charged particle beam 11 is changed before the change of the relative mirror position of the charged particle mirror 10.

[0063] In order to determine 750 the detection efficiency of the charged particle beam system 100 for multiple reflection angles 21, 22, 421, 521, the potential of the charged particle source 105 can be determined, for example, to adapt the landing energy of the primary charged particle beam. The signal strength of the detector signal of the signal charged particle beam 12 for each of the multiple positions of the charged particle mirror is associated with an estimated detector signal based on the landing energy of the primary charged particle beam. For each of the reflection angles 21, 22, 421, 521 and / or for each of the energies of the primary charged particle beam 11, the detection efficiency can be determined.

[0064] From the multiple detection efficiencies for multiple reflection angles and / or for multiple charged particle energies, a representation, in particular a mapping, describing the detection efficiency for different emission angles and different emission energies from the sample can be generated. The representation can be used to calibrate the measurement signal from the sample for different detection efficiencies at multiple emission angles.

[0065] In some embodiments, different charged particle beam systems 100 may be compared. In particular, different charged particle beam systems 100 may be compared to compensate for differences in detection efficiency and / or detection paths, in particular at the same energy of the same primary charged particle beam 11 or at the same reflection angle 21, 22, 421, 521. In some embodiments, the charged particle beam system 100 may be calibrated at regular intervals using a charged particle mirror 10.

[0066] In some embodiments, a metric describing the detection efficiency is formed. The metric can be used to correct the SEM image in a post-processing process, particularly in a process for determining a critical dimension of a sample. Advantageously, images taken at different charged particle beam systems 100 can be better matched. In some embodiments, an algorithm can use the metric to adjust a SEM image taken at one charged particle beam system 100 so that the grayscale of another charged particle beam system 100 matches, in particular, the reference charged particle beam system 100.

[0067] According to some embodiments, the charged particle optical components can be adjusted based on the representation of the signal beam characterization. For example, the optical elements in the charged particle beam system and / or the charged particle beam system can be aligned. In addition, the signal and / or primary charged particle beams can be aligned in the charged particle beam system based on the representation or mapping of the signal charged particle beam characterization. For example, the voltage and / or current at the deflector or corrector can be adjusted (and / or calibrated) based on the representation of the signal charged particle beam.

[0068] Specifically, the following embodiments are described herein:

[0069] Embodiment 1: A method for characterizing a detection path in a charged particle beam system having a primary charged particle beam, the method comprising: positioning a charged particle mirror having a curved equipotential surface on a sample stage of the charged particle beam system; changing the reflection angle of the primary charged particle beam at the curved equipotential surface by changing the relative mirror position of the charged particle mirror, wherein the curved equipotential surface is a certain distance away from the surface of the charged particle mirror; recording multiple detector signals of at least one detector of the charged particle beam system for multiple relative mirror positions; wherein changing the relative mirror position of the charged particle mirror comprises changing at least one of the mirror position of the charged particle mirror and the position of the primary charged particle beam relative to each other in at least one dimension.

[0070] Embodiment 2: A method as described in embodiment 1, wherein the curved equipotential surfaces are rotationally symmetric.

[0071] Embodiment 3: The method of any one of Embodiments 1 to 2, wherein the charged particle mirror comprises a mirror element, wherein the mirror element is rotationally symmetric.

[0072] Embodiment 4: The method of any one of embodiments 1 to 3, wherein the curved equipotential surface is a concave equipotential surface.

[0073] Embodiment 5: The method of any one of embodiments 1 to 3, wherein the curved equipotential surface is a convex equipotential surface.

[0074] Embodiment 6: The method as described in any one of Embodiments 1 to 5, further comprising: associating the reflection angle of the primary charged particle beam with at least one of the relative mirror positions of the charged particle mirror with respect to the primary charged particle beam.

[0075] Embodiment 7: The method as described in Embodiment 6 further comprises: correlating the reflection angle of the primary charged particle beam with at least one detector signal recorded at a corresponding relative mirror position of the charged particle mirror relative to the primary charged particle beam.

[0076] Embodiment 8: The method as described in Embodiment 7 further comprises: correlating the detection efficiency with the reflection angle of the primary charged particle beam.

[0077] Embodiment 9: The method of Embodiment 7, further comprising: creating a representation of at least one detector signal recorded at multiple reflection angles.

[0078] Embodiment 10: The method of Embodiment 9, wherein the representation comprises detector signals recorded at a plurality of energies of the primary charged-particle beam.

[0079] Embodiment 11: The method of Embodiment 9, further comprising: correcting the SEM image in a post-processing process based on a representation of at least one detector signal recorded at multiple reflection angles.

[0080] Embodiment 12: The method as described in any one of embodiments 1 to 11, further comprising: adjusting the mechanical position and / or voltage and / or current of the charged particle optical components of the charged particle beam system based on the representation of at least one detector signal recorded at multiple reflection angles.

[0081] Embodiment 13: The method as described in any one of Embodiments 1 to 12, further comprising: varying the energy of the primary charged particle beam.

[0082] Embodiment 14: The method of Embodiment 13, wherein the energy of the primary charged particle beam is varied without changing the arrangement of optical elements between the charged particle mirror and the detector.

[0083] Embodiment 15: The method of any one of Embodiments 13 to 14, wherein a plurality of detector signals are recorded for a plurality of energies of the primary charged particle beam for a plurality of relative mirror positions.

[0084] Embodiment 16: A method as described in any one of Embodiments 1 to 15, wherein changing the relative mirror position of the charged particle mirror relative to the primary charged particle beam includes changing the position of the charged particle mirror relative to the primary charged particle beam in at least two dimensions.

[0085] Embodiment 17: The method as described in any one of Embodiments 1 to 16, wherein changing the relative mirror position of the charged particle mirror with respect to the primary charged particle beam includes causing the primary charged particle beam to scan the charged particle mirror in at least two dimensions.

[0086] Embodiment 18: The method of any one of Embodiments 1 to 17, wherein the charged particle mirror comprises a support.

[0087] Embodiment 19: The method of Embodiment 18, wherein the pillar is recessed relative to a sample plane of the charged particle beam system.

[0088] Embodiment 20: A method as described in Embodiment 18, wherein the pillar is recessed relative to the sample plane of the charged particle beam system so that the reflection point of the charged particles is substantially equal to the sample plane at the center of the pillar.

[0089] Embodiment 21: A method as described in any of Embodiments 1 to 20, wherein the charged particle mirror comprises a mirror element, wherein the mirror element is a conductor, and wherein the potential of the mirror element is adjusted by a voltage source conductively connected to the charged particle mirror.

[0090] Embodiment 22: A method as described in any one of Embodiments 1 to 20, wherein the charged particle mirror comprises a mirror element, wherein the mirror element is insulating, and wherein the method as described in any one of Embodiments 1 to 20 further comprises: charging the mirror element with a charged particle beam until a predefined potential is reached.

[0091] Embodiment 23: The method of any one of Embodiments 1 to 20, wherein the mirror element comprises an insulator.

[0092] Embodiment 24: A charged particle mirror configured for characterizing a charged particle beam system according to the method as described in any of the preceding embodiments.

[0093] Embodiment 25: A charged particle mirror, comprising: a substrate; a mirror element, the mirror element having a pillar recessed relative to the surface of the substrate; wherein the pillar comprises at least one of the following items: a conductive connector, the conductive connector being configured to connect the pillar to a voltage source; a conductive element, the conductive element being configured to generate a curved equipotential surface when a voltage is applied; and wherein the pillar is rotationally symmetric.

[0094] Embodiments of the present disclosure provide one or more of the following advantages. A detection path can be characterized using charged particles that reflect at a defined angle. A detection path can be characterized using multiple reflection angles. A detection path can be characterized using charged particles that reflect at a defined energy. Characterizing the detection path allows grayscale matching. A charged particle mirror can provide a well-defined curved equipotential surface.

[0095] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope of the embodiments, and the scope of the embodiments is determined by the claims that follow.

Claims

1. A method of characterizing a detection path in a charged particle beam system having a primary charged particle beam, the method comprising: positioning a charged particle mirror having a curved equipotential surface on a sample stage of the charged particle beam system; changing the reflection angle of the primary charged particle beam at the curved equipotential surface by changing the relative mirror position of the charged particle mirror, the curved equipotential surface being at a certain distance from the surface of the charged particle mirror; and recording a plurality of detector signals of at least one detector of the charged particle beam system for a plurality of relative mirror positions; Wherein varying the relative mirror position of the charged particle mirror comprises varying at least one of a mirror position of the charged particle mirror and a primary charged particle beam position relative to each other in at least one dimension.

2. The method of claim 1, wherein the curved equipotential surfaces are rotationally symmetric.

3. The method of claim 1, wherein the charged particle mirror comprises a mirror element, the mirror element being rotationally symmetric. The method of claim 1 , wherein the curved equipotential surface is a concave equipotential surface. The method of claim 1 , wherein the curved equipotential surface is a convex equipotential surface.

6. The method according to any one of claims 1 to 5, further comprising: The reflection angle of the primary charged particle beam is associated with at least one of the relative mirror positions of the charged particle mirror with respect to the primary charged particle beam.

7. The method of claim 6, further comprising: The reflection angle of the primary charged particle beam is associated with at least one detector signal recorded at a respective relative mirror position of the charged particle mirror with respect to the primary charged particle beam.

8. The method of claim 7, further comprising: A detection efficiency is related to the reflection angle of the primary charged particle beam.

9. The method of claim 7, further comprising: A representation of the at least one detector signal recorded at a plurality of reflection angles is created.

10. The method of claim 9, further comprising: The SEM image is corrected in a post-processing process based on the representation of the at least one detector signal recorded over the plurality of reflection angles.

11. The method of claim 9, further comprising: At least one of a mechanical position, a voltage, and a current of a charged particle optics component of the charged particle beam system is adjusted based on the representation of the at least one detector signal recorded over the plurality of reflection angles.

12. The method according to any one of claims 1 to 5, further comprising: The energy of the primary charged particle beam is varied.

13. The method of claim 12, wherein the plurality of detector signals are recorded for a plurality of energies of the primary charged particle beam for a plurality of relative mirror positions.

14. The method of any one of claims 1 to 5, wherein varying the relative mirror position of the charged particle mirror relative to the primary charged particle beam comprises varying the position of the charged particle mirror relative to the primary charged particle beam in at least two dimensions.

15. The method of any one of claims 1 to 5, wherein causing the relative mirror position of the charged particle mirror relative to the primary charged particle beam to vary comprises causing the primary charged particle beam to scan the charged particle mirror in at least two dimensions.

16. The method of any one of claims 1 to 5, wherein the charged particle mirror comprises a support.

17. The method of claim 16, wherein the pillar is recessed relative to a sample plane of the charged particle beam system.

18. The method of claim 16, wherein the pillar is recessed relative to a sample plane of the charged particle beam system such that a reflection point of charged particles is substantially equal to the sample plane at a center of the pillar.

19. A method as claimed in any one of claims 1 to 5, wherein the charged particle mirror comprises a mirror element, wherein the mirror element is a conductor, and wherein the potential of the mirror element is adjusted by a voltage source conductively connected to the charged particle mirror.

20. The method of any one of claims 1 to 5, wherein the charged particle mirror comprises a mirror element, wherein the mirror element is insulating, and wherein the method of claim 1 further comprises: The mirror element is charged with a charged particle beam until a predefined potential is reached.

21. The method of any one of claims 1 to 5, wherein the charged particle mirror comprises a mirror element, and wherein the mirror element comprises an insulator.

22. A charged particle mirror configured for characterizing a charged particle beam system according to a method of characterizing a detection path in a charged particle beam system having a primary charged particle beam, the method comprising: positioning a charged particle mirror having a curved equipotential surface on a sample stage of the charged particle beam system; changing the reflection angle of the primary charged particle beam at the curved equipotential surface by changing the relative mirror position of the charged particle mirror, the curved equipotential surface being at a certain distance from the surface of the charged particle mirror; and recording a plurality of detector signals of at least one detector of the charged particle beam system for a plurality of relative mirror positions; Wherein varying the relative mirror position of the charged particle mirror comprises varying at least one of a mirror position of the charged particle mirror and a primary charged particle beam position relative to each other in at least one dimension.

23. A charged particle mirror, comprising: substrate; a mirror element having a support column recessed relative to a surface of the substrate; The pillars include at least one of the following: a conductive connector configured to connect the support post to a voltage source; a conductive element configured to generate a curved equipotential surface when a voltage is applied; and The struts are rotationally symmetric.

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